Such a mechanism is provided with a screw comprising an outer thread, with a nut disposed around the screw and comprising an inner thread, and with a plurality of longitudinal rollers that have an outer thread engaged with the outer and inner threads of the screw and of the nut.
In a first type of roller screw mechanism, the threads of the rollers and the thread of the nut have helix angles that are identical to one another and different from that of the thread of the screw, such that, when the screw rotates with respect to the nut, the rollers rotate on themselves and roll around the screw without moving axially inside the nut. The rollers are guided in rotation parallel to the axis of the screw by way of ring gears that are fitted in a non-threaded part of the nut and comprise inner synchronizing gear teeth engaged with outer gear teeth of the rollers. Such a mechanism is referred to as a planetary roller screw.
In order to reduce the number of parts to be manufactured and joined together, it is possible to form the inner synchronizing gear teeth directly on the nut, axially on either side of the thread of the nut.
However, with the current design of such mechanisms with gear teeth integrated in the nut, it is necessary to carry out first gear cutting operations in order to form in the bore of the nut one of the gear teeth on one side of the inner thread, then to turn the nut and subsequently carry out second gear cutting operations in this bore in order to form the other gear teeth on the opposite side. This succession of operations substantially increases the cost of manufacturing the nut.
Moreover, with such a method, angular misalignments generally occur between the two inner synchronizing gear teeth formed on the nut. Such misalignments can cause deformations of the rollers of the mechanism, mainly by torsion, or even deterioration of the gear teeth of these rollers.
A second type of roller screw mechanism has a similar operating principle, but differs by way of an inverted disposition. The helix angles of the threads of the rollers, of the screw and of the nut are chosen such that, when the screw rotates with respect to the nut, the rollers rotate on themselves about the screw and move axially in the nut. The rollers are guided in rotation by outer synchronizing gear teeth that are formed on the screw and engage with the gear teeth of the rollers. Such a mechanism is referred to as an inverted roller screw.
In order to manufacture the screw equipped with outer synchronizing gear teeth of such a mechanism, provision is also made of gear cutting operations for example with the aid of two radially acting hobs that are mounted on a common support spindle. The two hobs successively cut the two synchronizing gear teeth on the outer surface of the screw. The time for manufacturing the screw is relatively long. Moreover, during manufacture, angular misalignments of the teeth of one of the outer synchronizing gear teeth of the screw with respect to the teeth of the other gear teeth can occur in this case, too.